Physical activity (PA) has been identified as a national priority area for promoting the health of the US population. While the health benefits of an active lifestyle are well documented in adults, the prevalence of inactivity in the US adult population remains high. It is widely believed that the prevention of physical activity in adults is best accomplished by establishing a physically active lifestyle during youth that will persist into adulthood. However, there is a paucity of data on the relationship between childhood and adult physical activity and no evidence that an active child becomes an active adult. The overall goal of this study is to examine the relationship between physical activity in adolescence and physical activity in young adulthood. This proposal is a follow-up study of 1245 young adults aged 21-25 years, who represent a biracial population-based cohort initially recruited in 1990 to participate in a NIH funded longitudinal study of the incidence and determinants of injury in adolescents, the Asolescent injury Control Study (AICS).The baseline age of the participants was 12- 16 years of age. Extensive physical activity data were collected during the four years of AICS. Physical activity will be assessed in the current study using a standardized questionnaire identical to that used in the adolescent study. Additional data to be collected include sociodemographic (i.e., education, marital status, occupation), lifestyle factors (i.e., cigarette and alcohol use), and psychosocial factors (i.e., self- efficacy, social support, barriers), as well as health information. Data collected in this proposed study and data from AICS will be combined, allowing for longitudinal analyses of the same subjects from ages 12-16 (AICS bseline) to ages 25-29 (final year of proposed study). The primary objectives of this study are to: 1) determine changes in the amount of PA from adolescence to young adulthood and to evaluate possible gender and racial differences; 2) evaluate the degree of tracking of PA from adolescence to young adulthood; and 3) evaluate adolescent predictors of PA in young adulthood.